1. Field of the Invention
This invention relates to a restricted passage system usable for use in a vibration damping device enclosing an electrorheological fluid therein, and more particularly to a restricted passage system capable of having a sufficiently long passage length for ensuring a large damping force.
2. Description of the Related Art
For example, Japanese Patent laid open No. 1-135938 and No. 2-176230 disclose a vibration damping device enclosing an electrorheological fluid therein, in which a viscosity of the electrorheological fluid passing through electrodes in a restricted passage system can be increased in accordance with a voltage between the electrodes or an intensity of electric field to change a damping force.
In the device described in Japanese Patent laid open No. 1-135938, the restricted passage is a zigzag passage extending outward and inward in the radial direction, so that the full length of the passage and hence the length of the electrode can not be prolonged to a satisfactory length and consequently the given damping force can not be obtained. Furthermore, the restricted passage is fastened at its one end to a side of a fastening member and at the other end to a portion of a movable member to change a sectional area of the passage in accordance with a relative displacement between the fastening member and the movable member, so that there is a problem that the occurrence of stable damping force can not always be obtained.
In the device of the Japanese Patent laid open No. 2-176230, a full length of the restricted passage formed between a piston and a damper casing is short, so that there is caused a problem of causing no large damping force.